The structural simplicity of a helicopter rotor that allows the centrifugal loads, as well as all flapping, lead-lag, and torsional motions, to be carried by flexible structural elements (flexbeams) rather than by rolling-element or elastomeric bearings is attractive to the rotor designer. The development of composite materials in recent years has provided the necessary conditions for the design of rotors without bearings, but the apparent structural simplicity of a bearingless rotor conceals a number of difficult design problems, including the strain in a flexbeam element caused by combined deformations, aeromechanical stability, blade-pitch control, and redundant structural load paths.
The bearingless-rotor development efforts to date have been successful in demonstrating that the critical design problems with bearingless rotors can be overcome. However, with each of these development efforts, success in solving a particular design problem has usually been achieved at the expense of another design goal. For example, long fatigue life may be achieved but only by compromising the desired hub-moment stiffness goals.